HackBo / reflow_oven

Firmware and docs for new reflow oven

Reflow Oven

Firmware and docs for new reflow oven.

Project codename: Oven One :-)

Installing

In recent Ubuntu versions you'll need the following packages:

• python3
• python3-serial
• arduino

Thermocouple

We're using a WZP PT100. There is a table for it but you can summarize them with a quadratic equation.

Temperature	Resistance
0	100
100	138.51
200	175.86
300	212.05

Temperature =  0.001113 * r * r + 2.329774 * r - 244.0946281

A line wasn't enough to summarize the table.

Getting a voltage from the thermocouple

This StackOverflow answer was useful.

Using the following equation you can get one that gives you a voltage for different thermocouple resistance values.

This is a voltage divider.

Vout =  (Vin * R2) / (R1 + R2)

R2 = (Vout * R1) / (Vin - Vout)

We'll use Vin = 5v and we know R1's value, so the only variable is the thermocouple (R2).

For now we're using R1 = 221 ohms (what we measured).

Arduino Uno pinout

Analog inputs

• A0 : ADC input from the Vout formula above (Measuring Vout).

Digital outputs

• Pin 3 : Output port 0 (resistance)
• Pin 4 : Output port 1 (resistance)
• Pin 13 (built-in led): Fast blink for error condition (invalid command, for instance).

Protocol

Messages that are sent to the Arduino. Each command describes what is sent and what is sent back. All communications are in bytes.

• 0 : Select first port. Returns '0' (byte).
• 1 : Select second port. Returns '1' (byte).
• • : Turns on selected port. Returns '+'.
• • : Turns off selected port. Returns '-'.
• A : Asks for ADV value of selected port. Returns 'A', and then the ADC value in two bytes (first one is the highest one).

You can select 0 and 1 to do pings to the device. Recommended after startup.

Power Circuit

[easy eda project] (https://easyeda.com/cmsvalenzuela/Power_circuit_reflow_oven-b03160d6e52648cb9ea1c21ea43c88d2).

Max 6675 type k thermocouple